THe SPERMATOGENESIS OF DOMESTIC MAMMALS. 375 
Pyrrhocoris, with comparative review of the type of sexual differences of the chromosome- 
groups. Ibid. Vol. VI 
, (1913): Achromatoid body simulating an accessory chromosome in Pentatoma. Biol. 
Bull. Vol. XXIV. 
WODSEDALER, J. E., (1913): Spermatogenesis of the pig with special reference to the accessory 
chromosomes, Biol. Bull, Vol. XXV. 
, (1914): Spermatogenesis of the horse with special reference to the accessory chromo- 
some and chromatoid body. Ibid. Vol. XXVIL. 
Yocom, B., (1917): Some Phases of spermatogenesis in the mouse. Am. Calif. Publ. 
EXPLANATION OF FIGURES. 
All figures were drawn with the aid of a camera lucida, using a Zeiss1/12 objective and a 
compensating ocular 12, except Figs, 1—4 which were drawn with a Zeiss 5 ocalar and Figs. 5, 6 
with a Zeiss 4 ocular. The following abbreviations have been employed: 
a. ch,— accessory chromosome. ch. c,—chromatoid corpuscle. 
i. ¢,—interstitial cell. mt,—mitochondria. 
s. sc,—Sertoli-cell. 
PLATE XL 
Figs. 1—3. Section of the testis of a young animal. 
Fig. 4. Metaphase plates of primary spermatogonia. 
Figs. 5, 6. Section of the testis of an adult animal (3 years old). 
Figs. 7, 8. Primary spermatogonia in resting stage. 
Fig. 9. Prophase of a primary spermatogonium. 
Fig. 10, Polar view of a metaphase plate of a primary spermatogonium. 
Fig. 11. Lateral view of metaphase plate of a secondary spermatogonium. 
Fig. 12. Anaphase of a secondary spermatogonium. 
Figs. 13—15. Resting primary spermatocytes. 
Fig. 16. Presynaptic stage (leptotene stage). 
Figs. 17, 18. Synapsis, showing parallel arrangement of chromatin threads. 
Fig. 19. Postsynaptic stage; complete fusion occurs between the pairing threads 
Fig. 20. Postsynaptic stage. 
Figs. 21, 22. Spermatocytes in late postsynaptic stage. 
PLATE XL. 
Figs. 23, 24. Spermatocytes in late postsynaptic stage, showing mitochondrial granules. 
Figs. 25—27. Successively later postsynaptic stages. 
Figs. 28—30. Prophases ot first reduction division. 
Fig. 31. Polar view of metaphase of first division. . 
